Definition
Published IFR routes designated by Air Traffic Control for use at or above 18,000 feet MSL (the high-altitude structure, Class A airspace), intended to organize and streamline traffic flow between busy airport pairs. Pilots are expected to file these routes when planning flights between city pairs for which a high altitude preferred route is published.
Plain English
These are recommended flight paths that ATC wants pilots to use when flying high — at or above 18,000 feet — between certain busy airports. Filing one of these routes makes it more likely your flight plan will be accepted as filed without changes.
Context Anchor
You will see high altitude preferred routes during IFR flight planning, especially when choosing a route between busy airports or through busy airspace.
Derivation
"Preferred" here means preferred by ATC, not by the pilot. The system designates these routes because using them keeps traffic flowing predictably through the high-altitude structure.
Why Pilots Care
Using these routes increases the likelihood that a filed flight plan will be approved without changes, improving efficiency and predictability.
Analogy
Think of it like a recommended highway route through a busy city. You may be able to ask for another way, but the published preferred route is the one traffic managers expect most aircraft to use.
Intuition Check
“Preferred” does not mean the pilot’s personal favorite route. Here it means a route published because air traffic control prefers it for managing traffic. “High altitude” does not just mean “fairly high.” In this context it points to the high-altitude instrument route system, generally around 18,000 feet and above.
Example Sentence 1
Planning a flight from Chicago to Atlanta at FL370, the pilot checked the Chart Supplement and filed the published high altitude preferred route between the two airports.
Example Sentence 2
Checking the high altitude preferred routes helped avoid potential delays during peak traffic hours.